Please update media-gfx/scantailor package to version 0.9.12.2 that was released May 2, 2016. Because we have in tree really old version (2012 year), thanks. Bear in mind that maintainer of app in upstream was changed and they make some fixes, so probably we don't need patches from current tree version anymore, thanks. https://github.com/scantailor/scantailor/releases
Thanks. https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=f17a5c062e0a6755f90d70827fb25f7bdd515bf6